His comments, a day after the United States and Europe moved to lift sanctions on Iran following a July nuclear deal, coincide with ramped up efforts to attract international oil majors back to Tehran.

Sanctions relief could unlock Iran, which has the world's largest combined oil and gas reserves, from decades of under-investment and stifled production.

But emerging opportunities come after a string of corruption scandals in which middlemen were allegedly co-opted by past governments to circumvent oil sanctions, pocketing commissions.

One of them, Babak Zanjani, currently on trial for fraud and economic crimes, is accused of pocketing USD 2.8 billion (2.5 billion euros) during former president Mahmoud Ahmadinejad's tenure.

Zanjani could face the death penalty if he is convicted.

The oil minister urged foreign investors to deal directly with his ministry, rather than using third parties to find their way into the Islamic republic's abundant energy market.

"We despise the corrupt parasites that want to suck the nation's blood even in this situation," he said, to loud applause at an oil and energy industry event in the capital.

"They will tell you that until you give us our commission you can't get your work done. Don't believe them," he added.

Iran will hold a conference in Tehran on November 21-22 to unveil new contract terms designed to tempt foreign companies back.

Despite renewed interest since the July 14 nuclear deal between Iran and Britain, China, France, Russia and the United States plus Germany, a precipitous fall in international oil prices in the past year and market glut may cause energy firms to hold off.